Write a C function to count number of nodes in a given singly linked list.
For example, the function should return 5 for linked list 1->3->1->2->1.
Iterative Solution
1) Initialize count as 0
2) Initialize a node pointer, current = head.
3) Do following while current is not NULL
a) current = current -> next
b) count++;
4) Return count
C++ Programming:
// Iterative C program to find length or count of nodes in a linked list
#include<stdio.h>
#include<stdlib.h>
/* Link list node */
struct node
{
int data;
struct node* next;
};
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
void push(struct node** head_ref, int new_data)
{
/* allocate node */
struct node* new_node =
(struct node*) malloc(sizeof(struct node));
/* put in the data */
new_node->data = new_data;
/* link the old list off the new node */
new_node->next = (*head_ref);
/* move the head to point to the new node */
(*head_ref) = new_node;
}
/* Counts no. of nodes in linked list */
int getCount(struct node* head)
{
int count = 0; // Initialize count
struct node* current = head; // Initialize current
while (current != NULL)
{
count++;
current = current->next;
}
return count;
}
/* Drier program to test count function*/
int main()
{
/* Start with the empty list */
struct node* head = NULL;
/* Use push() to construct below list
1->2->1->3->1 */
push(&head, 1);
push(&head, 3);
push(&head, 1);
push(&head, 2);
push(&head, 1);
/* Check the count function */
printf("count of nodes is %d", getCount(head));
return 0;
}
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Output:
count of nodes is 5
Recursive Solution
int getCount(head)
1) If head is NULL, return 0.
2) Else return 1 + getCount(head->next)
C++ Programming:
// Recursive C program to find length or count of nodes in a linked list
#include<stdio.h>
#include<stdlib.h>
/* Link list node */
struct node
{
int data;
struct node* next;
};
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
void push(struct node** head_ref, int new_data)
{
/* allocate node */
struct node* new_node =
(struct node*) malloc(sizeof(struct node));
/* put in the data */
new_node->data = new_data;
/* link the old list off the new node */
new_node->next = (*head_ref);
/* move the head to point to the new node */
(*head_ref) = new_node;
}
/* Counts the no. of occurences of a node
(search_for) in a linked list (head)*/
int getCount(struct node* head)
{
// Base case
if (head == NULL)
return 0;
// count is 1 + count of remaining list
return 1 + getCount(head->next);
}
/* Drier program to test count function*/
int main()
{
/* Start with the empty list */
struct node* head = NULL;
/* Use push() to construct below list
1->2->1->3->1 */
push(&head, 1);
push(&head, 3);
push(&head, 1);
push(&head, 2);
push(&head, 1);
/* Check the count function */
printf("count of nodes is %d", getCount(head));
return 0;
}
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Output:
count of nodes is 5